The World's Nuclear Test Watchdog

May 11, 1986|By Rolf Soderlind, United Press International

STOCKHOLM, SWEDEN — It really shouldn't be surprising that the Swedes alerted the world about the Chernobyl nuclear accident. Sweden for some time now has been tuned in to Soviet nuclear activity on another level -- nuclear weapons testing.

A supersensitive listening post lets Swedish seismological watchdogs keep track of most underground nuclear tests in the Soviet Union, and anywhere else in the world as well.

The only way the Soviets could cheat, said Nils-Olov Bergkvist, is ''if they set off a really small explosion in a cavity created by a previous test. ''From Semipalatinsk the Soviet test site we register explosions down to one kiloton,'' he said. One kiloton is 1,000 tons of TNT.

Bergkvist and others sense Soviet -- and American -- nuclear tests mainly from an ordinary red-and-white wooden house that looks like tens of thousands scattered around Sweden.

Only a nearby antenna reveals that this two-story house is special. In fact it is the Hagfors observatory, Sweden's best seismological station, rising on a forest hill near Hagfors village in western Sweden.

The observatory uses seismometers placed in holes drilled into Sweden's bedrock granite to measure underground shock waves from nuclear tests and earthquakes. The granite is geographically and geologically ideal for the purpose.

Hagfors is one of 16 unmanned seismological stations that automatically feed seismic data to the spider in the web, a computer at the national defense research agency headquarters in Stockholm, where Bergkvist is based.

''Hagfors is surely one of the world's best seismological stations.'' Bergkvist said.

The Hagfors station is perfect for measuring underground tests, he said, especially those carried out 2,500 miles away at Semipalatinsk, Soviet's main military test site in central Asia.

It also monitors U.S. nuclear blasts from the Nevada desert test site, 5,100 miles away, ''but it takes an explosion yielding over 15 kilotons for us to discover it,'' Bergkvist said.

The United States conducted 12 to 19 secret nuclear tests from 1982 through 1984, according to the Natural Resources Defense Council, a private American research group that based its calculations on seismic data provided by Hagfors and other sources.

The United States and the Soviet Union each carry out about 15 military tests a year, Bergkvist said. The United States reports its tests but the Soviets never announce their tests.

No superpower test detected by Hagfors has exceeded the 1974 Threshold Test Ban Treaty, he said, although the Reagan administration has said the Soviets probably have violated the treaty, which limits underground tests to no more than 150 kilotons.

Hagfors detected 30 military and peaceful nuclear explosions last year, a 40 percent drop from 1984 because of the moratorium on tests proclaimed by Moscow last July 30.

The Reagan administration rejected the moratorium, saying the Soviets had made the offer only for propaganda because their own current test series was finished.

The Soviet Union announced an end to its moratorium April 11, a day after the latest U.S. test. The Soviet military said it suffered setbacks during the unilateral moratorium.

U.S. officials noted that the last time Washington accepted such a Soviet offer, in 1961, Moscow ended the silence with the largest series of explosions the world has ever seen. They included the Oct. 30, 1961, ''Doomsday'' atmospheric test -- a 58-megaton blast equal to 3,000 Hiroshima bombs.